Abstract: An underwater card gap test method was proposed to measure shock sensitivity of explosives by combining the underwater explosion method and the small card gap test. The shock sensitivity of six explosives, which included PETN, RDX, 8701, Desensitized RDX, TNT, expanded ammonium nitrate explosive, was measured by the proposed underwater card gap test method.The experimental results show that the shock sensitivity of six explosives including PETN, RDX, 8701, Desensitized RDX, TNT and expanded ammonium nitrate get down successively. The results by the underwater card gap test method were compared with the results by the traditional gap test and the results from literatures. Comparison indicates that the experimental results are believable. Furthermore, effect of charge density on shock sensitivity of explosives was investigated by the underwater card gap test method.